It's the debt for irrelevant education. You don't need a million Pokemon scholars, and society would do much better if they had gone into engineering instead.

Colleges used to be finishing schools for the rich attached to educational institutions for geniuses (the geniuses keep the prestige level up, and the rich provide funding). Companies started demanding degrees to get people who are geniuses or well-connected, so new schools popped up to produce more graduates, and so on in a feedback loop. Eventually the degree became a requirement and not a signal of "eliteness" any more. The people getting the degrees still feel elite, even though many go on to become baristas and store clerks.

The problem is that college was never about the education (except for a small minority of students who were usually in the sciences), it was always about the signaling. The part that we think is good (the education) is just a side effect.